Silk series two includes Peake's character spending the night in the officers' mess and Penry-Jones will get his clothes off Photograph: Colin Hutton/BBC

Twelve years ago Channel 4 launched a drama series set in a barristers' chambers, featuring Rupert Penry-Jones and a female character who returned to work three days after having a baby. North Square acquired a devoted following among barristers, but never returned for a second series. "There was a change of regime at Channel 4," says the writer, Peter Moffat. "It was hugely loved and not watched by many people."

Moffat is the writer and Penry-Jones and Phil Davis are back in the cast, but Silk - whose second series opened this week - is not North Square 2. The cases are bigger, the lawyers are older and the setting is London rather than Leeds. The show's popularity among lawyers as well as the public suggests that this time Moffat has found his audience. Occasional legal grumbles about accuracy persist (Tuesday's episode showed a judge directing a jury to convict a defendant) but Twitter was probably more interested in a teasing line from new arrival Caroline Warwick, who declared she sometimes "swims in the ladies' pond".

Warwick, played by Frances Barber, is a silk 20 years' Martha Costello's senior. "She comes from a time when being at the bar as a woman would have been enormously tough," says Moffat. "She's paid a price for how hard she's had to work. She says to Martha that women at the bar have got to stick together, but then she says: 'Sometimes women at the bar don't like me because I'm sisterly out of court, and vicious in it.'"

The first series of Silk ended with Costello (Maxine Peake) taking silk but miscarrying her baby after being assaulted by a former client.

"It was a bit fortunate about that," says Moffat. He didn't want to portray Martha struggling between motherhood and career. "I think it's become quite a hackneyed thing on telly. I kind of wanted a character who wasn't doing that. And so staying away from the stereotype was the cause of the miscarriage. I don't know how the hell she was going to do it."

It certainly was hard to imagine her doing it: although a few of the last round of QC appointments were women with small children, neither of us could think of more than one single mother at the bar. Moffat clearly relishes the idea that Costello could be a role model.

"I'd like people to think, 'Oh my goodness how exciting, I wish I could do that. Maybe I can.' Or 'I'm a woman, I'm from the north, I can be like Maxine Peake.' That you don't have to walk in and be brilliant."

In the second episode, Costello represents an army officer at a military tribunal (Matthew McNulty) accused of killing a civilian in Afghanistan. "He's incredibly good-looking," Moffat divulges. Does Costello agree?

"Actually, she finds another soldier incredibly good looking. She spends a night in the officers' mess." Penry-Jones, meanwhile, "gets his clothes off" - though not, one assumes, in the ladies' pond.

Moffat's next drama series, which is still in development, is likely to be a rather more sober offering. His wife works in family law and he wants to portray what goes on in the family courts.

"I'm just so struck by how traumatising these experiences become for all the protagonists. For years and years people's lives are about fighting over a child, who's becoming more and more damaged as a consequence. I think it's terrible ... There are cases where all the lawyers involved know what the outcome is going to be. There are lawyers who are responsible for dragging things out too long."

Part of the appeal of the subject lies in the closed nature of the family courts. Moffat is in favour of Ken Clarke's decision to allow summings-up and sentencing remarks to be televised, but wonders whether the public will feel justice has been done after watching such a small part of the process.

"I think our courts feel undemocratic. You feel anxious about being there: as a member of the public, you feel that you're going to do something wrong." He points out how few non-lawyers ever visit the Temple: "You see maybe three people there on a Sunday. They feel they're not allowed in."

That reluctance to talk about the workings of the criminal justice extends to barristers' working lives. Many viewers, he says, were shocked by how little time Costello had to prepare for a case.

"I was surprised that people hadn't quite grasped how enormous the pressure is ... There are so many brilliant barristers and there are some really terrible ones as well. And that gives you an enormous amount of freedom."